The sense of smell is caused by odorants activating olfactory sensory neurons in the nose. A pivotal question in the field is how these neuronal activities give rise to odor perceptions. Since the neuronal architecture of the olfactory system i remarkably similar between insects and mammals, studying how the fly brain processes olfactory information could shed light on principles underlying olfaction in other organisms. We previously demonstrated that the olfactory cortex (lateral horn) is divided into two broad domains, one representing food odors and one representing pheromones. Therefore, this olfactory region, which to the naked eye looks homogenous, might be organized into olfactory processing centers that reflect biologically relevant information. These studies were based on simple classifications of odorants as being food or pheromone, but did not take into account the valence of the odorant - that is if it is behaviorally attractive or repulsive. Preliminary data frm our recent work suggests that aversive odors might represent a new processing center in the olfactory cortex. Using a combination of genetics, behavioral analyses, axon tracing, and brain imaging studies, we will test the hypothesis that (1) the olfactory cortex is organized into domains based on three important aspects of a fly's life: food, pheromones, and avoidance. Results from this work will allow us to link repulsive behaviors to their underlying neuronal components and thus model how newly identified and known aversive signals might be represented in the higher olfactory cortex. To understand how attractive signals such as attractive food odors and attractive pheromones are represented in the olfactory cortex, as well as how the olfactory system utilizes them to communicate relevant information regarding an animal's environment, we investigate a novel pheromone signaling system that we have identified. Our preliminary data suggests that this signaling system in Drosophila represents a behavioral link between food and pheromone signaling. Using a combination of genetics, molecular biology, GC-MS, calcium imaging, and electrophysiological recordings, we will test the hypothesis that (2) Drosophila secrete an attractive pheromone when stimulated by attractive food odors to tag sites for positive social behaviors such as egg laying or courtship. Results from the characterization of this new pheromone signaling mechanism will enrich our understanding of how olfactory communications are used to guide behavioral responses to a changing environment. The proposed studies are significant because we will gain insights into how aversive and attractive olfactory information is represented in higher processing centers of an olfactory system that could serve as a model for how olfactory perceptions are encoded in the brains of other animals. !